Linkage between Accretion Disks and Blazars

The magnetic field in an accretion disk is estimated assuming that all of the angular momentum within prescribed accretion disk radii is removed by a jet. The magnetic field estimated at the base of the jet is extrapolated to the blazar emission region using a model for a relativistic axisymmetric jet combined with some simplifying assumptions based on the relativistic nature of the flow. The extrapolated magnetic field is compared with estimates based upon the synchrotron and inverse Compton emission from three blazars, MKN 501, MKN 421 and PKS 2155-304. The magnetic fields evaluated from pure synchrotron self- Compton models are inconsistent with the magnetic fields extrapolated in this way. However, in two cases inverse Compton models in which a substantial part of the soft photon field is generated locally agree well, mainly because these models imply magnetic field strengths which are closer to being consistent with Poynting flux dominated jets. This comparison is based on estimating the mass accretion rate from the jet energy flux. Further comparisons along these lines will be facilitated by independent estimates of the mass accretion rate in blazars and by more detailed models for jet propagation near the black hole.Comment: Submiteed to the Astrophysics & Space Science special issue on the 5th Stromlo Symposiu

Predictors of mortality in adult patients with congenital heart disease

Background: Most patients with congenital heart disease (CHD) reach adulthood thanks to the successful efforts of cardiac surgeons. However, sudden cardiac deaths are significantly more prevalent in this population, and survival is reduced when compared to the general population. The aim of this study is to define the prognostic value of selected clinical parameters to predict mortality in adult CHD patients referred to the specialist outpatient centre. The following parameters were analyzed as potential predictors of long-term survival: complexity of heart defect, past surgical intervention, heart failure (functional class according to NYHA > I), cyanosis, age and gender. Methods: We analyzed data gathered from 1,304 patients (568 male) aged 18 to 72 (mean 29.4 ± 10.6) between 1995 and 2004. Mean duration of follow-up was 3.52 ± 1.83 years. Results: During follow-up, 29 deaths were recorded (2.2%). Higher mortality was found in the group of patients with complex as oppposed to simple CHD (28 [6.7%] vs. 1 [0.1%]; p = 0.00001), in subjects without surgical correction as opposed to those operated on (21 [6.1%] vs. 8 [0.8%], p = 0.00001). General survival was 99.1% at two years and 96.6% at five years. In univariate survival analysis, all single clinical variables except patient gender were associated with increased risk of death (p = 0.00001 for all). All patients who died presented with heart failure. In multivariate analysis, the independent predictor of mortality was cyanosis (heart rate 38.1). Complexity of lesion (heart rate 6.4) represented a relative risk factor. Conclusions: Heart failure and cyanosis are negative predictors of survival in adult patients with CHD. Complexity of the lesion increases the relative risk of mortality. Past cardiac surgery is associated with better survival, but, as with age and gender, it is not a significant prognostic factor

The cyclo-synchrotron process and particle heating through the absorption of photons

We propose a new approximation for the cyclo-synchrotron emissivity of a single electron. In the second part of this work, we discuss a simple application for our approximation, and investigate the heating of electrons through the self-absorption process. Finally, we investigate the self-absorbed part of the spectrum produced by a power-law population of electrons. In comparison to earlier approximations, our formula provides a few significant advantages. Integration of the emissivity over the whole frequency range, starting from the proper minimal emitting frequency, gives the correct cooling rate for any energy particle. Further, the spectrum of the emission is well approximated over the whole frequency range, even for relatively low particle energies (beta << 0.1), where most of the power is emitted in the first harmonic. In order to test our continuous approximation, we compare it with a recently derived approximation of the first ten harmonics. Finally, our formula connects relatively smooth to the synchrotron emission at beta=0.9. We show that the self-absorption is a very efficient heating mechanism for low energy particles, independent of the shape of the particle distribution responsible for the self-absorbed synchrotron emission. We find that the energy gains for low energy particles are always higher than energy losses by cyclo-synchrotron emission. We show also that the spectral index of the self-absorbed part of the spectrum at very low frequencies differs significantly from the well known standard relation I(nu) ~ nu^(5/2).Comment: 9 pages, 4 figures, accepted for publication in A&

Constraints to Energy Spectra of Blazars based on Recent EBL Limits from Galaxy Counts

We combine the recent estimate of the contribution of galaxies to the 3.6 micron intensity of the extragalactic background light (EBL) with optical and near-infrared (IR) galaxy counts to set new limits on intrinsic spectra of some of the most distant TeV blazars 1ES 0229+200, 1ES 1218+30.4, and 1ES 1101-232, located at redshifts 0.1396, 0.182, and 0.186, respectively. The new lower limit on the 3.6 micron EBL intensity is significantly higher than the previous one set by the cumulative emission from resolved Spitzer galaxies. Correcting for attenuation by the revised EBL, we show that the differential spectral index of the intrinsic spectrum of the three blazars is 1.28 +- 0.20 or harder. These results present blazar emission models with the challenge of producing extremely hard intrinsic spectra in the sub-TeV to multi-TeV regime. These results also question the reliability of recently derived upper limits on the near-IR EBL intensity that are solely based on the assumption that intrinsic blazar spectra should not be harder than 1.5.Comment: 13 pages, 2 figures, submitted to the Astrophysical Journa

Implications of automatic photon quenching on compact gamma-ray sources

Aims: We investigate photon quenching in compact non-thermal sources. This involves photon-photon annihilation and lepton synchrotron radiation in a network that can become non-linear. As a result the gamma-ray luminosity of a source cannot exceed a critical limit that depends only on the radius of the source and on the magnetic field. Methods: We perform analytic and numerical calculations that verify previous results and extend them so that the basic properties of photon quenching are investigated. Results: We apply the above to the 2006 TeV observations of quasar 3C279 and obtain the parameter space of allowed values for the radius of the emitting source, its magnetic field strength and the Doppler factor of the flow. We argue that the TeV observations favour either a modest Doppler factor and a low magnetic field or a high Doppler factor and a high magnetic field.Comment: 10 pages, 12 figures, accepted for publication in Astronomy and Astrophysic

X-ray variability patterns in blazars

We study the expected variability patterns of blazars within the two-zone acceleration model putting special emphasis on flare shapes and spectral lags. We solve semi-analytically the kinetic equations which describe the particle evolution in the acceleration and radiation zone. We then perturb the solutions by introducing Lorentzian variations in its key parameters and examine the flaring behavior of the system. We apply the above to the X-ray observations of blazar 1ES 1218+304 which exhibited a hard lag behavior during a flaring episode and discuss possibilities of producing it within the context of our model. The steady-state radio to X-rays emission of 1ES 1218+304 can be reproduced with parameters which lie well within the ones generally accepted from blazar modeling. Additionally, we find that the best way to explain its flaring behavior is by varying the rate of particles injected in the acceleration zone.Comment: accepted by A&

Switched Current Sigma-Delta Modulator with a New Comparator Structure Designed Based on VHDL-AMS Description

The paper presents a VHDL-AMS based approach to the Switched-Current (SI) Sigma-Delta Modulator design. The prototype VHDL-AMS description, with the help of elaborated EDA tools, is automatically translated into the SI realization. Another tool helps the designer to create the layout. The paper also describes a new current mode comparator, which is used in the design. Postlayout simulation results are presented